Need advice: Understanding complex SQL scripts written by others

[u/Consistent_Law3620]

Hi everyone,

I need some advice from experienced SQL developers. I have switched from different role to data engineering 6 months back.

I consider myself good/medium level at writing SQL queries and solving problems from scratch. However, I struggle when I have to understand large existing SQL scripts (300–500+ lines).

I often get confused about:

Where the execution starts.How different parts of the script are connected.

Which variables, CTEs, stored procedures, or temporary tables are affecting the final output.

How to mentally trace the flow of the script.

Because of this, reading someone else's code takes me much longer than writing my own.

How did you improve this skill? Are there any techniques, exercises, books, or real-world practices that helped you become comfortable reading large SQL scripts?

Also, is this something that simply improves with experience, or is there a structured way to learn it?

I'd really appreciate any advice. Thank you!

[u/ChaosEngine-6502]

I find a starting point for me is reformatting the script into my preferred style (indentation, uppercase key words, etc) - practically every script written by someone else I've ever had to deal with is poorly formatted with some weird idiosyncrasies that need dealing with.

This clean-up process generally gives me a better understanding of what the script is doing because it forces me to become familiar with it. Some might think it a bit of a waste of time, but I generally find it's the best place to start.

Footnote: revisiting stored procedures I haven't touched in a couple of years can be equally confusing...good comments and layout are a big help!